Nickel electroplating bath with additives



Un ted t es. P te Q I 3,305,461 NICKEL ELECTRORLATING BATH WITH ADDITIVES Barnet l). Ostrow, 125 Redwood Drive, and Fred I. Nobel, 75 Fem Drive, both of Roslyn, NY. 11576 No Drawing. Filed Aug. 23, 1963, Ser. No. 304,270 9 Claims. (Cl. 204-49) the major difiiculties associated with nickel baths emacetylenic derivatives are exceptionally prone to skipping, clouding and hazing. By skipping is meant, the inability of the nickel electroplating bath to cover with nickel, parts in low current density areas.

There has been described the addition to the bath of thiomalic acid to overcome this difiiculty. It has been found, however, that compounds of this category are not eiiective in overcoming such skipping tendencies. Although the thiomalic acids increase the tolerance of the electroplating bath to such metallic impurities as lead and Zinc, it will not overcome the skipping tendencies that are imparted by higher concentrations of acetylenic derivatives. Since the acetylenic derivatives impart the maximum luster and leveling to the plating bath, it is desirable to keep them in a fairly high concentration to obtain the optimum brilliance and leveling. In many cases this concentration of acetylenic derivatives is such that the low current density areas for example, areas as loW as 1 amp/sq. ft. or less are then not covered by the nickel electroplate. Since in modern electroplating it is essential from a commercially feasible application to have the nickel electroplate cover the low current density areas, as Well as the high, it becomes necessary frequently to operate these nickel'baths with less than the optimum concentration of the acetylenic compounds in order to secure coverage in these low current densities. This, of course, results in deposits that do not have the maximum leveling or brightening rate.

When the acetylenic compounds are added to the bath at their optimum concentration, or in excess of the optimum concentration, in addition to skipping, these high concentrations of acetylenic compounds also impart hazes and clouds to the deposit. These hazes and clouds are sometimes corrected by the addition of sulfooxygen compounds. These compounds must generally be added in fairly large quantities and they in turn adversely afiect the leveling. In any event the sulfo-oxygen compounds do not overcome the tendency to skip, whereas they may correct the clouding and hazing concentrations.

In modern bright nickel plating, the acetylenic derivatives, even in lower than optimum concentration, may

3,335,461 Patented Feb. 21, .1967

under electrolysis, form degradation productions that tend to give gray to black low current density recessed areas.

This condition is particularly more pronounced when trace amounts of zinc, lead or copper are present as impurities. Since commercial bright nickel plating involves plating of zinc die castings, as well as copper plated and copper base metal parts, the tendency for contamination with these metals, is always present and may become serious.

In US. Patent No. 2,361,720, it has been suggested that thiopyrimidines be used in nickel plating baths as brightening agents. Specifically a compound mentioned has been 2 mercapto-4,6,alkyl-6-dihydroxypyrimidine. To increase the solubility, these products are sul-fated or sulfonated. In addition, the use of the aforementioned pyrimidines in conjunction with sulfonated aryl aldehydes has been described. Although the pyrimidines and the pyrimidines in combination with sulfonated aryl aldehydes produced bright plate, these deposits exhibited no leveling. Actually, the pyrimidines, when used in concentrations sufiicient to impart overall brightness, tended to produce negative leveling. When used in conjunction with sulfo-oxygen compounds, the pyrimidines behaved in a similar manner.

The present invention is adapted and intended to overcome the difiiculties inherent in prior compositions of the type discussed above, it being among the objects of the invention to provide an aqueous acid nickel plating bath having certain additives therein which will avoid skipping in the low current density areas.

It is also among the objects of the invention to provide such a composition which will prevent or at least greatly limit the tendency of baths of this type to form hazy or cloudy depositsf It is further'among the objects of the present inven tion to provide such a composition which will impart to the deposit a maximum of luster and a high degree of leveling.

It has now been found that the combination of mercapto alkyl hydropyrimidines in conjunction with acetylenic compounds, overcome the tendency for these compounds to skip. Usually the alkyl groups have from 1 to 4 carbon atoms. In addition, when used in combination with sulfo-oxygen compounds, the acetylenic derivatives in conjunction with the mercapto alkyl pyrimidines produce bright plate without haze, cloud and skip, without impairment of the leveling characteristics. Therefore, unlike the pyrimidines used in conjunction with suite-oxygen compounds alone, the combination of the mercapto pyrimidines with the acetylenic derivatives and the sulfo-oxygen compound, will produce deposits that are level and bright, without any of the aforementioned undesirable characteristics. The tolerance of the acetylenic base baths to zinc, copper or lead is greatly enhanced by the addition of the mercapto pyrimidine. Since the mercapto pyrimidines are not too soluble in the system, we prefer to use the sulfonated or sulfated type of derivatives. It is only through the combination of these three ingredients that the maximum improvements can be secured.

Compounds typical of the sulfo-oxygen compounds are such sulfonamids and sulfonimides as o-benzene sulfonimid (Na salt), benzene sulfonamid, dibenzene sulfonimid, p-toluene sulfonamid, benzene sulfahydroxamic acid (Na salt), and allyl sulfonamid. Among sulfonic acids are naphthalene trisulfonic acid (Na salt), benzene sulfonic acid (Ni salt), benzene vinyl sulfonic acid (Na salt), allyl sulfonic acid (Na salt), naphthalene 1,5 disulfonic acid (Na salt), l-butene sulfonic acid, quinoline sulfonic acid, and pyridine sulfonic acid. Of the above sulfonamids and sulfonimids are presently preferred.

Typical acetylenic derivatives are Z-methyl 3-butyne 2-01, 1,4 butyne diol, 1,4 diethoxy butyne diol, propargyl alcohol, butynoxyacetic acid, N,N,N propargyl triethylene tetramine, and N,N,N propargyl diethylene triamine. Typical mercapto pyrimidines includes '2-mercapto 4,6 diethyl 4-methyl dihydro pyrimidine, sulfonated 2-mercapto 4,6 diethyl 4-methyl dihydro pyrimidine, Z-mercapto 4,4,6 trimethyl dihydro pyrimidine, Z-mercapto 4,6 dimethyl dihydro pyrimidine, and sulfonated Z-mercapto 4,4,6 trimethyl dihydropyrimidine.

These combinations may be included in a standard Watts Formulation of the following composition or in a high chloride formulation of the following type of composition.

NiSO '6H O, g./1. 100-300 NiCl -6H O, g./l. 30-100 H BO g./l. 2060 pH 3.0-4.8

Temperature, F.

The preferred bath is one with NiSO '6H O 300 g./l., NiCl -6H O 90 g./l., H 80 45 g./l., pH 4.0-4.5, and temperature l35140 F. with mild agitation. To the baths above is added such surface active agents as are commonly employed in the art to decrease surface tension and reduce pitting. Examples of such surfactants are sodium lauryl sulfate, sodium octyl sulfate, sodium octyl sulfonate, and sodium lauryl sulfoacetate.

The mercapto pyrimidines may be used in concentrations as low as 0.001 gram per liter. The amounts of sulfonamides, sulfonamids and the sulfonic acids may be present in the solution in the bath in amounts of about 0.2 gram per liter and up to saturation. The higher concentrations will be determined by the quantity of acetylenic compound that is present in the bath as well as the type of acetylenic compound. Generally a sufficient quantity of the mercapto pyrimidine is added to overcome the skipping or low current density problem. For example, the standard Watts type solution containing 1 gram per liter of saccharine and 0.4 gram per liter of methylbutynol, with the nickel solution being agitated, will show a tendency toward low current density skipping. The addition of 0.01 gram per liter of the sulfonated derivative of 4,4,6,trimethyl 2-mercapto dihydropyrimidine will increase the coverage of the nickel in the low current density, substantially eliminating the skip without impairing the luster and level of the bright nickel plate.

Using a bath of the following composition will illustrate the combination usage of these additives:

G./l. NiSO -7H O 300 NiCl -6H O 45 H3BO3 45 Sodium lauryl sulfate 0.2

Grams Per Liter The concentrations of the several additives may be greatly varied as other concentrations than those set forth are workable with good effects. The preferred range of the acetylenic compound is from .001 to 1.0 gram per liter, and the concentration of the mercapto pyrimidine is from .001 to 1.0 gram per liter, but the invention is not restricted to these specific amounts.

What is claimed is:

1. An aqueous acid nickel plating bath having incorporated therein a water soluble acetylenic compound and a water-soluble mercapto alkyl hydropyrimidine, the amount of said compounds being sufficient to prevent skip plate in low current density areas.

2. A nickel plating bath according to claim 1 characterized in that said bath contains also a substance taken from the class consisting of aromatic sulfonamids, sulfonimids, and sulfonic acids in sufficient amounts to produce leveling of deposits without clouding.

3. A nickel plating bath according to claim 2 characterized in that said substance is present in amounts of 0.2 gram per liter to saturation.

4. A nickel plating bath according to claim 2 characterized in that said acetylenic compound is present in amounts of .001 to 1.0 gram per liter.

5. A nickel plating bath according to claim 2 characterized in that said mercapto-pyrimidine is present in amounts of .001 to 1.0 gram per liter.

6. A nickel plating bath according to claim 1 characterized in that said acetylenic compound is present in amounts of .001 to 1.0 gram per liter.

7. A nickel plating bath according to claim 1 characterized in that said mercapto-pyrirnidine is present in amounts of .001 to 1.0 gram per liter.

8. A nickel plating bath according to claim 1 characterized in that said pyrimidine contains at least one hydro group.

9. A nickel plating bath according to claim 1 characterized in that said pyrimidine contains a plurality of alkyl groups.

References Cited by the Examiner UNITED STATES PATENTS HOWARD S. WILLIAMS, Primary Examiner. JOHN H. MACK, Examiner.

G. KAPLAN, Assistant Examiner. 

1. AN AQUEOUS ACID NICKEL PLATING BATH HAVING INCORPORATED THEREIN A WATER SOLUBLE ACETYLENIC COMPOUND AND A WATER-SOLUBLE MERCAPTO ALKYL HYDROPYRIMIDINE, THE AMOUNT OF SAID COMPOUNDS BEING SUFFICIENT TO PREVENT SKIP PLATE IN LOW CURRENT DENSITY AREAS. 